Despite appeals for calm from the crash victims' families, rioters torched a library, a tax office and damaged dozens of shops and businesses, police said.

Five police officers were seriously hurt, one of whom was hit by a projectile apparently fired from a hunting rifle.

Police made five arrests and responded with tear gas, rubber bullets and paint guns designed to identify troublemakers. Spent cartridges, broken glass and rocks thrown by rioters littered the streets and about 60 vehicles were torched.

In the 2005 unrest, thousands of cars were torched after two teenagers were electrocuted when they climbed into a power sub-station while apparently fleeing police.

Authorities have opened an investigation into the deaths of the two youths on Sunday night. The local prosecutor's office said the incident was ''a traffic accident'' but some questions remained over how quickly help arrived.